Night's Bright Lights Dim View for Remote Telescopes

Below:

Next story in Science

LONG BEACH, Calif. — Humans have looked up to the night skies and
seen thousands of glittering stars since the dawn of time, but
streetlights and illuminated signs have increasingly obscured
that majestic view. Now astronomers are saying those lights
increasingly pose problems for even the most remote telescopes.

Blue light-emitting diodes (LED) pose the most serious threat,
because blue light scatters much more in the atmosphere than
other wavelengths and often heads right back down toward giant
telescopes.

Artificial light "decreases astronomers' ability to see faint
objects, makes the effective size of telescopes smaller and makes
some observations impossible," Richard Wainscoat, an astronomer
at the University of Hawaii, said here at the
221st annual meeting of the American Astronomical Society.

Bright nights, big cities

Stargazing has
been a beloved pastime for millennia. Ancient people marked the
seasons and the months using constellations, and associated
celestial bodies with heavenly gods.

"There's a growing social need to turn the night into daytime,
and that's basically destroyed the normal average citizen's stars
at night," Wainscoat told LiveScience. "There's whole generations
of people who see five or 10 stars at night."

Light fixtures installed in the 1980s were usually sodium-based,
and emitted a yellowish glow. Newer streetlights are starting to
use LEDs, which emit blue light, a much bigger problem for
astronomers and other skywatchers.

Unlike yellower light, blue light scatters in the atmosphere like
pinballs, and often heads right back to the ground.

Mauna Kea Observatory, a telescope perched on a mountain 13,700
feet (4,200 meters) above sea level, is protected somewhat from
light
pollution by its height and the clouds that shroud the
valleys below. But Chile's iconic telescopes, such as the Atacama
Large Millimeter Array (ALMA), are seeing increased light
pollution on the horizon from nearby towns and cities.

And in Arizona, telescopes like the
Kitt Peak Observatory have had to contend not just with light
pollution from Phoenix and Tucson, but also large blue light LED
billboards that were illegally installed throughout the state,
said Richard Green, an astronomer at the University of Arizona.

Preserving night skies

To reduce light pollution,
streetlights should be completely shielded so that light
doesn't leak out the sides, Green said.

Rays emitted slightly above horizontal will bounce around the
atmosphere, while light angled downward mostly leaves the
atmosphere. This measure can also improve glare and save money
through energy efficiency, because less light is being "wasted"
pointing upward.

In addition, towns and cities can advocate for filters on blue
light LEDs. In general, blue light is hard on the eyes, so
filtering the most damaging wavelengths can make the night
environment more pleasant, Wainscoat said.

Using artificial illumination only when needed, for instance, by
installing motion-sensitive lights, can also darken the night skies.
Light curfews and tighter local ordinances requiring
context-appropriate lighting (an example would be preventing
giant billboards from installing lights that glow in an otherwise
dark locale) are also critical, Green said.

And local and national governments can do a better job of
enforcing light ordinances already on the books. For instance,
the northern provinces of Chile, which have several of the
world's most cutting-edge telescopes already have tight rules on
when, where, and what type of lights can be installed, but with
no enforcement, those rules are often flouted, Green said.